1. Field of the Invention
The present invention relates generally to an external control type fan-coupling device, in which an engine cooling fan rotation in an automobile or the like is controlled according to the temperature change in the surrounding, the change in the running condition of the engine or the like.
2. Description of the Related Art
In the prior art, there is a fan-coupling device of this kind, wherein the inside of a sealed housing composed of a case and a cover is divided by a partition having an oil feed adjusting hole into an oil sump and a torque transmission chamber housing a drive disc therein, wherein a dam formed is in such a portion, in which the oil accumulates at a rotating time, of the inner circumference wall face of the sealed housing side confronting the outer circumference wall portion of the drive disc, wherein an oil circulation passage is formed to lead to the dam between the torque transmission chamber and the oil sump, and wherein a valve member is provided for opening the feed adjusting hole of the partition when the temperature or the like of the surrounding is higher than a set value and for closing the feed adjusting hole of the partition when not higher than the set value, whereby the effective contact area of oil at a torque transmission clearance portion formed in the wall face, as confronting the drive disc, in the outer vicinity of the sealed housing is increased/decreased to control the torque transmission from the drive side to the sealed housing on the driven side. A pair of electromagnets are provided on the front side or the back side of the sealed housing, and a valve member having a magnetism for opening/closing the feed adjusting hole is proposed to confront one of the electromagnets (as referred to Japanese Patent No. 2911623 and JP-A-3-61727).
In the case of the external control type fan-coupling device of the prior art, however, the electromagnets for activating the valve member and the armature are separated by the case of the non-magnetic member so that the magnetic force cannot be efficiently transmitted to the armature. An excessive electromagnetic force is needed for attracting the armature. There arise problems that the size and weight of the electromagnets are enlarged, that the fan-coupling device cannot be reduced in size and weight, and that more power consumption is needed. If the armature is located at a position spaced from the rotary shaft in the oil sump, moreover, there arises a defect that the action of the armature, i.e., the activity of opening/closing the valve member is deteriorated by the resistance of the oil because the armature always exists in the oil while the fan is rotating.